Light emitting diodes (“LEDs”) have attracted much attention due to many advantages, such as small volume, low power consumption, long lifetime, fast-response, environmental friendliness, and high reliability etc. They are used widely in indicating lamps, decorating lamps, signal lamps etc. It can be looked forward to the coming future that LEDs will access into general lighting field with the faster and advanced developments.
Generally, there are two ways to generate white LED: one way is to combine the red, green and blue LEDs to get white light; the other way is to excite phosphors with LED to obtain white light. According to the difference in phosphors, the latter approach includes three routes: matching yellow phosphor with blue LED, matching green and red phosphors with blue LED, or matching red, green and blue phosphors with purple or UV LEDs.
As for current LED techniques, white LEDs are preferred to be generated by incorporating blue LED with YAG (yttrium aluminum garnet) yellow phosphor. In the Chinese patent CN97196762, this phosphor is reported in details. However, due to the characteristics of the phosphor, the luminous efficiency of white LEDs using this YAG phosphor is not yet adequate at present, and it is not applicable in general lighting field by taking into account the energy-saving. Therefore, the studies on novel phosphors with good luminescence performance are focused by many researchers from all over the world.
A silicate-borate phosphor represented by the formula (Y,La)1-x-y-zCexGdyTbz(Mg,Zn,Gd)1-pMnpB5-q-s(Al,Ga)qXsO10 has been reported in the German patent DE19730005. Phosphors comprising silicon, disclosed in British patents GB1334838, GB1326868 and GB1379949, with emission main peaks at 370-430 nm, are employed as cathode ray exciting phosphors. An alkaline-earth silicate phosphor that can be excited by blue light to generate yellow light, with similar performance as that of the YAG phosphor, has been developed by Barry (J. Electrochem. Soc., 1968, 115: 1181-1184), and has been described in white LED in U.S. Patent Publication US20040051111.